1. Field of the Invention
The present invention relates to a magnetoresistive thin-film magnetic element that undergoes a change in electrical resistance in relation to the magnetization vector of a pinned magnetic layer and the magnetization vector of a free magnetic layer affected by an external magnetic field, and to a method for making the same. The present invention also relates to a thin-film magnetic head equipped with the magnetoresistive thin-film magnetic element.
2. Description of the Related Art
FIG. 24 is a perspective view of an exemplary conventional thin-film magnetic head.
This thin-film magnetic head is a floating thin-film magnetic head used with a magnetic recording medium such as a hard disk device. A slider 251 of the thin-film magnetic head has a reading side 235 and a trailing side 236. Longitudinal air bearing surfaces (ABS) 251a and 251b and air grooves 251c are formed on the surface of the slider 251 facing the disk.
A magnetic core unit 250 is provided on an end face 251d of the slider 251.
The magnetic core unit 250 of this thin-film magnetic head is a composite-type thin-film magnetic head having the structure shown in FIGS. 25 and 26, and is formed by successively depositing an MR (read head) h1 and an inductive head (write head) h2 on the trailing end face 251d of the slider 251.
The magnetoresistive head h1 comprises a lower shield layer 253 which is formed on the trailing side portion of the slider 251 and is composed of a magnetic alloy, a lower gap layer 254 formed on the lower shield layer 253, a magnetoresistive thin-film magnetic element layer 245 formed on the lower gap layer 254, an upper gap layer 256 formed on the magnetoresistive thin-film magnetic element layer 245, and an upper shield layer 257 formed on the upper gap layer 256. The upper shield layer 257 also serves as a lower core layer of the inductive head h2 formed thereon.
The MR head reads the information stored in the recording medium by detecting a change in resistance at the magnetoresistive thin-film magnetic element layer 245 occurred in response to a weak leakage magnetic field from the magnetic recording medium such as a disk in a hard disk device.
The inductive head h2 includes a lower core layer 257, a gap layer 264 formed on the lower core layer 257, and a coil layer 266 patterned in a spiral. The coil layer 266 is surrounded by a first insulation layer 267A and a second insulation layer 267B. An upper core layer 268 is formed on the second insulation layer 267B. At the air bearing surface 251b, a magnetic pole end portion 268a of the upper core layer 268 is arranged to face the lower core layer 257 with a magnetic gap G therebetween. As shown in FIGS. 25 and 26, a base end portion 268b of the upper core layer 268 is magnetically connected to the lower core layer 257.
A protective layer 269 composed of alumina or the like is provided on the upper core layer 268.
In this inductive head h2, a recording current flows to the coil layer 266 and from the coil layer 266 to the core layers. The inductive head h2 writes magnetic signals onto a magnetic recording medium such as a hard disk by using a leakage magnetic field provided from the end portions of the lower core layer 257 and upper core layer 268 at the magnetic gap G.
A giant magnetoresistive element (GMR element) or the like is provided in the magnetoresistive thin-film magnetic element layer 245. The GMR element has a multi-layer structure using a combination of several different materials. Among structures which generate giant magnetoresistive effects, a spin-valve type which is relatively simple in structure while achieving a high rate of change in resistance, is known in the art. There are a single spin-valve type and dual spin-valve type in the spin-valve type.
FIG. 27 is a cross-sectional view of a principal portion of an exemplary thin-film magnetic head MR2 equipped with a conventional spin-valve thin-film magnetic element, viewed from the side facing a recording medium.
The spin-valve thin-film magnetic element MR2 is a bottom-type single spin-valve thin-film magnetic element comprising an antiferromagnetic layer 122, a pinned magnetic layer 153, a nonmagnetic conductive layer 124, and a free magnetic layer 165, deposited in that order from the bottom.
In FIG. 27, a composite all has a substantially trapezoidal shape and includes an underlayer 121 comprising Ta or the like, the antiferromagnetic layer 122 composed of a PtMn alloy formed on the underlayer 121, the pinned magnetic layer 153 formed on the antiferromagnetic layer 122, the nonmagnetic conductive layer 124 formed on the pinned magnetic layer 153, the free magnetic layer 165 formed on the nonmagnetic conductive layer 124, and a protective layer 127 formed on the free magnetic layer 165. The antiferromagnetic layer 122 extends to the region corresponding to the two lateral portions of the pinned magnetic layer 153, the nonmagnetic conductive layer 124, and the free magnetic layer 165.
The pinned magnetic layer 153 is composed of a nonmagnetic interlayer 154, a first pinned magnetic sublayer 155, and a second pinned magnetic sublayer 156, the latter two sandwiching the nonmagnetic interlayer 154. The first pinned magnetic sublayer 155 is provided at the position closer to the antiferromagnetic layer 122 than is the nonmagnetic interlayer 154, and the second pinned magnetic sublayer 156 is provided at the position closer to the nonmagnetic conductive layer 124 than is the nonmagnetic interlayer 154.
The first pinned magnetic sublayer 155 and the second pinned magnetic sublayer 156 comprise elemental Co, a CoFe alloy, a NiFe alloy, or the like. The nonmagnetic interlayer 154 comprise a nonmagnetic material such as Ru.
Preferably, the thickness of the first pinned magnetic sublayer 155 and the thickness of the second pinned magnetic sublayer 156 are different from each other. In FIG. 27, the thickness of the second pinned magnetic sublayer 156 is greater than the thickness of the first pinned magnetic sublayer 155.
An exchange coupling magnetic field (exchange anisotropic magnetic field) is generated at the interface between the first pinned magnetic sublayer 155 and the antiferromagnetic layer 122. The magnetization vector of the first pinned magnetic sublayer 155 is pinned in the direction opposite to the Y direction in the drawing by the exchange coupling magnetic field with the antiferromagnetic layer 122. The second pinned magnetic sublayer 156 antiferromagnetically couples with the first pinned magnetic sublayer 155 so as to pin the magnetization vector of the second pinned magnetic sublayer 156 in the Y direction.
Since the magnetization vectors of the first pinned magnetic sublayer 155 and the second pinned magnetic sublayer 156 are antiparallel to each other, magnetic moments of the first pinned magnetic sublayer 155 and the second pinned magnetic sublayer 156 cancel out. However, because the thickness of the second pinned magnetic sublayer 156 is greater than the thickness of the first pinned magnetic sublayer 155, the spontaneous magnetization of the second pinned magnetic sublayer 156 slightly remains thereby putting the pinned magnetic layer 153 in a ferri-magnetic state. Moreover, the slight spontaneous magnetization further intensifies the exchange coupling magnetic field with the antiferromagnetic layer 122, pinning the magnetization vector of the pinned magnetic layer 153 in the Y direction in the drawing.
The free magnetic layer 165 includes an antiferromagnetic layer 166 comprising a ferromagnetic material such as a NiFe alloy and an anti-diffusion layer 167 composed of a ferromagnetic material such as Co. The anti-diffusion layer 167 is provided on the nonmagnetic conductive layer 124.
Hard bias layers 126 comprising a Coxe2x80x94Pt-type alloy, i.e., permanent magnetic layers, are provided at two sides of the free magnetic layer 165 and on the extended portions of the antiferromagnetic layer 122. Bias underlayers 175 comprising Cr are provided to separate the hard bias layers 126 and the antiferromagnetic layer 122. Each of the bias underlayers 175 is provided under each of the hard bias layers 126 and between the composite MR2 and the hard bias layers 126 at the two sides thereof.
Conductive layers 128 comprising Cr, Ta, Au, or the like are deposited on the hard bias layers 126 so as to supply a detection current to the free magnetic layer 165, the nonmagnetic conductive layer 124, and the pinned magnetic layer 153.
The hard bias layers 126 prevent Barkhausen noise generated when a plurality of magnetic domains are formed in the free magnetic layer 165 and put the free magnetic layer 165 in a single-magnetic-domain state. When the hard bias layers 126 are magnetized in the X1 direction in the drawing, a leakage magnetic field from each of the hard bias layers 126 orients the magnetization vector of the free magnetic layer 165 in the X1 direction in the drawing. Accordingly, the variable magnetization vector of the free magnetic layer 165 and the pinned magnetization vector of the pinned magnetic layer 153 are set to be substantially orthogonal to each other.
By forming the bias underlayers 175, the axis of magnetic induction of the Coxe2x80x94Pt-type alloy constituting the hard bias layers 126 is oriented in the planar direction, thereby improving the characteristics such as coercive force, remanence ratio, and the like, of the hard bias layers 126 as the permanent magnetic layers. Thus, significantly large bias magnetic field can be generated, thereby putting the free magnetic layer into a single-magnetic-domain state and inhibiting generation of Barkhausen noise.
In this spin-valve thin-film magnetic element MR2, a detection current (sense current) is supplied from the conductive layers 128 to the free magnetic layer 165, the nonmagnetic conductive layer 124, and the pinned magnetic layer 153. The recording medium such as a hard disk moves in the Z direction in the drawing. When there is a leakage magnetic field from the magnetic recording medium, the magnetization vector of the free magnetic layer 165 changes from the Y direction to the X1 direction in the drawing. At this time, spin-dependent scattering of conduction electrons occurs at the interface between the nonmagnetic conductive layer 124 and the free magnetic layer 165 and at the interface between the nonmagnetic conductive layer 124 and the second pinned magnetic sublayer 156, causing a change in electrical resistance. Accordingly, the leakage magnetic field from the recording medium is detected as the change in electrical resistance.
Moreover, although the magnetic moments of the antiferromagnetically coupled first and second pinned magnetic layers 155 and 156 do cancel out each other, the spontaneous magnetization of the second pinned magnetic sublayer 156 remains slightly because the thickness of the second pinned magnetic sublayer 156 is greater than the thickness of the first pinned magnetic sublayer 155, putting the pinned magnetic layer 153 in a ferri-magnetic state. The spontaneous magnetization further intensify the exchange coupling magnetic field with the antiferromagnetic layer 122, pinning the magnetization vector of the pinned magnetic layer 153 in the Y direction in the drawing. As a consequence, the spin-valve thin-film magnetic element MR2 enjoys a stable performance.
In the conventional spin-valve thin-film magnetic element MR2, because the bias underlayers 175 are provided between the free magnetic layer 165 and the hard bias layers 126 arranged at the two sides of the free magnetic layer 165, the free magnetic layer 165 and the hard bias layers 126 are not magnetically and directly connected. Thus, the only magnetic field applied to the free magnetic layer 165 is that of the magnetostatic interaction, i.e., the effective magnetic field applied from the hard bias layers 126 (static magnetic field). This magnetic field alone controls the magnetic domain of the free magnetic layer 165 and puts the free magnetic layer 165 into a single-magnetic-domain state.
Demagnetizing fields B in the two end portion of in the track width Tw direction of the free magnetic layer 165 applies, to the two side portions of the free magnetic layer 165, a magnetic field opposite to a desired direction. This leads to a so-called xe2x80x9cbuckling phenomenonxe2x80x9d in which the magnetization vectors at the two side portions of the free magnetic layer 165 become disordered and discontinuous developing domain walls therein. The demagnetizing field B is a magnetic field acting in the opposite direction of the magnetization vector of the free magnetic layer 165 due to the magnetic charges accumulated in the two side portions of the free magnetic layer 165.
In recent years, demand for higher recording density has led to a narrower track width in the magnetoresistive head h1. As the track width becomes narrower, the demagnetizing field in the two side portions of the free magnetic layer 165 intensifies, undesirably promoting the buckling phenomenon and degrading the magnetic domain controllability in the free magnetic layer 165. As a consequence, a output waveform become erroneous at the two side portions of the track width Tw and there is a problem of increased instability in the output waveform.
One way to minimize the buckling phenomenon is to increase the thickness of the hard bias layers so as to intensify the magnetic field (bias magnetic field) for saturating the free magnetic layer 165, thereby removing the influence of magnetic charges accumulated in the two side portions of the free magnetic layer 165. In this way, however, the read output at the center portion of the composite all tends to be high and the read output at the side portions of the composite tends to be low. In this respect, when the thickness of the hard bias layers are increased, the regions located at the side portions with low read output become larger, degrading the overall read output. This problem becomes more salient as the track becomes narrower.
Accordingly, it is an object of the present invention to provide a magnetoresistive thin-film magnetic element having high output waveform stability in the two ends of the track width. In the magnetoresistive thin-film magnetic element, a bias magnetic field from the hard bias layers is not undesirably high, thereby improving the read output. The bias magnetic field may be effectively applied to the free magnetic layer from the hard bias layers, and disorder of the magnetization vectors at the two side portions of the free magnetic layer due to a demagnetizing field occurred in the two side portions of the free magnetic layer may be prevented. The magnetic domains of the free magnetic layer may be satisfactorily controlled. Another object of the present invention is to provide a method for making the magnetoresistive thin-film magnetic element having the above-described advantages.
Yet another object of the invention is to provide thin-film magnetic head equipped with the magnetoresistive thin-film magnetic element having the above-described advantages.
To these ends, a magnetoresistive thin-film magnetic element according to a first aspect of the invention includes a composite having an antiferromagnetic layer, a pinned magnetic layer, the magnetization vector thereof being pinned by an exchange anisotropic magnetic field with the antiferromagnetic layer, a nonmagnetic conductive layer formed between the pinned magnetic layer and a free magnetic layer; hard bias layers, formed on two sides of the free magnetic layer so that at least part of each of the hard bias layers is in direct contact with the free magnetic layer, for orienting the magnetization vector of the free magnetic layer in a direction substantially orthogonal to the magnetization vector of the pinned magnetic layer; a conductive layer for supplying a sense current to the free magnetic layer, the nonmagnetic conductive layer, and the pinned magnetic layer; and bias underlayers each being provided under each of the hard bias layers, for controlling crystal orientation of the hard bias layers.
In this magnetoresistive thin-film magnetic element, the hard bias layers and the free magnetic layers are in contact with each other at least partly. Thus, the free magnetic layer and the hard bias layers at the two sides thereof may be magnetically coupled by an exchange coupling (exchange interaction), inhibiting the generation of a demagnetizing field at the two side portions of the free magnetic layer. As a consequence, a strong bias magnetic field may be applied to the free magnetic layer from the hard bias layers, and the disorder of the magnetic vectors at the two side portions due to the demagnetizing field may be prevented (prevention of a buckling phenomenon). The magnetic domains of the free magnetic layer may be satisfactorily controlled, improving the stability of the output waveform at the two ends of the track width.
An exchange interaction between the free magnetic layer and the hard bias layers at the two sides thereof acts between the spinning magnetic atoms and is a significantly strong interaction which orients the magnetization vectors in parallel to each other. This strong interaction effectively removes the magnetic charges accumulated in the two side portions of the free magnetic layer 21, thereby inhibiting the generation of the demagnetizing field at the two side portions of the free magnetic layer. Moreover, since the bias underlayers for controlling the crystal orientation of the hard bias layers are formed at the bottom of the hard bias layers, the crystal orientation of the hard bias layers is satisfactory, the coercive force and the remanence ratio being sufficiently large. Thus, the intensity of the bias magnetic field required for putting the free magnetic layer 21 in a single-domain state may be sufficiently increased and generation of Barkhausen noise may be prevented.
Furthermore, since no demagnetizing field occurs in the two side portions of the free magnetic layer, the buckling phenomenon may be inhibited even when the track width of the read head equipped with the spin-valve thin-film magnetic element may be made narrower. Thus, the output waveform at the two ends of the track width Tw may be prevented from becoming erroneous by the buckling phenomenon which would otherwise occur, and the instability of the overall read head may be reduced.
Also, even when the product of the remanence and the thickness of the hard bias layers is reduced to a certain extent, the above-described exchange interaction prevents the demagnetizing field from occurring in the two side portions of the free magnetic layer. The bias magnetic field from each hard bias layer may be effectively applied to the free magnetic layer, thereby securing the stability of the output waveform at the two ends of the track width Tw. In this respect, for example, the thickness of the hard bias layer may be decreased so as to decrease the exchange bias magnetic field. The region at the side portions of the composite, that is, the region with a lower read output, may be minimized so as to enlarge the region at the center portion having high read output, thereby improving the read output.
Preferably, the above-described magnetoresistive thin-film magnetic element according to the first aspect of the invention is of a dual type in which the nonmagnetic conductive layer, the pinned magnetic layer, and the antiferromagnetic layer are provided on each of two sides in the thickness direction of the free magnetic layer.
This magnetoresistive thin-film magnetic element has two sets of the free magnetic layer, the nonmagnetic conductive layer, and the pinned magnetic layer. Compared to the magnetoresistive thin-film magnetic element having only one set of these, a relatively high rate in change of resistance xcex94R/R may be obtained, meeting the demand for high recording density.
Preferably, the composite further includes a nonmagnetic interlayer which separates at least one of the pinned magnetic layer and the free magnetic layer into two sublayers, wherein the two divided sublayers are in a ferri-magnetic state in which magnetization vectors of the two divided sublayers are antiparallel to each other.
When the pinned magnetic layer is divided into two sublayers by a nonmagnetic interlayer, one of the two sublayers pins the magnetic vector of the pinned magnetic layer in a predetermined direction and maintains the pinned magnetic layer in a stable state.
When the free magnetic layer is divided into two sublayers by a nonmagnetic interlayer, an exchange coupling magnetic field is generated between the divided sublayers to be in a ferri-magnetic state. As a result, the magnetic thickness may be decreased, and the free magnetic layer rotates in an external field with high sensitivity.
In the magnetoresistive thin-film magnetic element according to one aspect, the bias underlayers may extend to the interfaces between the free magnetic layer and the hard bias layers provided at the two sides of the free magnetic layer.
In this magnetoresistive thin-film magnetic element, the hard bias layers and the free magnetic layers are in contact with each other at least partly even when the bias underlayers extend to the interfaces between the free magnetic layer and the hard bias layers at the two sides thereof. The free magnetic layer and the hard bias layer are magnetically coupled due to an exchange interaction, effectively removing the cause of a demagnetizing field, i.e., the magnetic charges accumulated at the two side portions of the free magnetic layer. Although the efficiency of the bias magnetic field applied from the hard bias layers to the free magnetic layer is decreased compared to the spin-valve thin-film magnetic element having the bias underlayers without portions extending to the interfaces between the free magnetic layer and the hard bias layers, a strong bias magnetic field may still be suitably applied from the hard bias layers to the free magnetic layer. Thus, the magnetization vectors in the two side portions of the free magnetic layer may be prevented from being disordered due to the demagnetizing field which would otherwise be generated at the two side portions of the free magnetic layer. The magnetic domains of the free magnetic layer may be suitably controlled and the stability of the read waveform at the two sides of the track width Tw may be improved.
Preferably, in this spin-valve thin-film magnetic element, the thickness of the extensions of the bias underlayers is preferably about 1 nm or less, and more preferably, about 0.5 nm or less.
When the thickness of the extensions is about 1 nm or less, pinholes are readily formed in the bias under layer. The free magnetic layer and the hard bias layers are magnetically coupled through these pinholes in the extensions of the bias underlayers. Accordingly, not only part of the free magnetic layer and the hard bias layers directly in contact with each other but also part of the free magnetic layer and the portion hard bias layers separated by the extensions of the bias underlayers are magnetically coupled. Moreover, since the region having the exchange interaction is enlarged, the magnetic charges accumulated in the two side portions of the free magnetic layer are effectively removed by the above-described exchange interaction, thereby inhibiting the demagnetizing field in the two side portions of the free magnetic layer. Thus, a strong bias magnetic field may be applied from each of the hard bias layers to the free magnetic layer, inhibiting the magnetization vectors in the two side portions of the free magnetic layer from being disordered due to the demagnetizing field which would otherwise occur at the two side portions of the free magnetic layer. As a result, the magnetic domains of the free magnetic layer may be further satisfactorily controlled and the stability of the read waveform at the two ends of the track width Tw can be further improved.
Preferably, the bias underlayers include a nonmagnetic metal having a body-centered cubic structure, and the hard bias layers are made of Cr. When the hard bias layers are composed of a Coxe2x80x94Pt-type alloy or a Coxe2x80x94Ptxe2x80x94Cr-type alloy, the crystal structure of the hard bias layers includes both the face-centered cubic structure (fcc) and the close-packed hexagonal structure (hcp). In this case, when the bias underlayers are composed of Cr having a body-centered cubic structure (bcc) and a (100) crystal orientation, the Coxe2x80x94Pt alloy or the Coxe2x80x94Ptxe2x80x94Cr alloy barely forms an fcc structure but readily forms a hcp structure because the lattice constants of the Cr layer and lattice constants of the Coxe2x80x94Pt alloy or the Coxe2x80x94Ptxe2x80x94Cr alloy are very close. The c axis (magnetization easy axis) of the hcp structure at this time is preferentially oriented in the planar direction of the interface between the Cr layer and one of the Coxe2x80x94Pt alloy layer and the Coxe2x80x94Ptxe2x80x94Cr alloy layer. Since an increased magnetic anisotropy is generated in the c axis of the hcp structure compared to the fcc structure, a larger coercive force (Hc) is generated when a magnetic field is applied to the hard bias layers. Furthermore, because the c axis of the hcp structure is preferentially oriented in the planar direction of the interface between the Cr layer and one of the Coxe2x80x94Pt alloy layer and the Coxe2x80x94Ptxe2x80x94Cr alloy layer, a remanence (Br) is increased and a remanence ratio (remanence (Br)/saturation flux density (Bs)) is also increased. As a result, the characteristics of the hard bias layers as the permanent magnetic layers are improved, intensifying the bias magnetic field generated from each of the hard bias layers, thereby readily aligning the free magnetic layer 21 into a single-magnetic-domain state.
Preferably the nonmagnetic metal having the body-centered cubic structure includes at least one metal selected from the group consisting of Cr, Ti, Mo and W50Mo50.
Preferably, slope angles at the side portions of the composite sandwiched by the hard bias layers are about 30 degrees or more to reduce the Barkhausen jump (BHJ) to about 15% or less. More preferably, the slope angles are about 45 degrees or more to reduce the BHJ to about 10% or less. Most preferably, the slope angles are about 60 degrees or more to reduce the BHJ to about 5% or less.
When the slope angle xcex8 is less than about 30 degrees, the end portion of the hard bias layer facing the composite becomes angular. As a consequence, the thickness of the end portion decreases while enlarging the end portions not provided with the bias underlayers at the bottom. In other words, the end portions having disordered crystal orientations are increased. The volume of the each portion having a reduced coercive force increases, thereby changing the magnetization state of the hard bias layer, and the bias magnetic field becomes disordered, thereby increasing Barkhausen jump (BHJ). It is then impossible to stably provide a sufficient bias magnetic field to the free magnetic layer, resulting in increased Barkhausen noise.
A magnetoresistive thin-film magnetic element according to another aspect includes a composite having an antiferromagnetic layer, a pinned magnetic layer the magnetization vector thereof being pinned by an exchange anisotropic magnetic field with the antiferromagnetic layer, a nonmagnetic conductive layer formed between the pinned magnetic layer and a free magnetic layer; hard bias layers formed at two sides of the composite, for orienting the magnetization vector of the free magnetic layer in a direction substantially orthogonal to the magnetization vector of the pinned magnetic layer; a conductive layer for supplying a sense current to the free magnetic layer, the nonmagnetic conductive layer, and the pinned magnetic layer; and bias underlayers each being provided under each of the hard bias layers and extends to the interface between the free magnetic layer and each of the hard bias layers, for controlling crystal orientation of the hard bias layers, in which the thickness of each of the hard bias underlayers is smaller at the interface between the free magnetic layer and each of the hard bias layers than under the hard bias layers.
Because the thickness of the hard bias layers is smaller at the interface between the free magnetic layer and each of the hard bias layers than under the hard bias layers, pin holes are formed in the portions of the bias underlayers sandwiched by the free magnetic layer and the hard bias layers. The free magnetic layer and the hard bias layer are magnetically coupled through these pinholes due to an exchange interaction, effectively removing the cause of a demagnetizing field, i.e., the magnetic charges accumulated at the two side portions of the free magnetic layer. A strong bias magnetic field can be suitably applied from the hard bias layers to the free magnetic layer, and the magnetization vectors in the two side portions of the free magnetic layer are prevented from being disordered due to the demagnetizing field which would otherwise be generated at the two side portions of the free magnetic layer. The magnetic domains of the free magnetic layer may be suitably controlled and the stability of the read waveform at the two sides of the track width Tw may be improved.
Preferably, the magnetoresistive thin-film magnetic element according to the second aspect of the invention is of a dual type in which the non magnetic conductive layer, the pinned magnetic layer, and the antiferromagnetic layer are provided on each of two sides in the thickness direction of the free magnetic layer.
This magnetoresistive thin-film magnetic element has two sets of the free magnetic layer, the nonmagnetic conductive layer, and the pinned magnetic layer. Compared to the magnetoresistive thin-film magnetic element having only one set of these, a relatively high rate in change of resistance xcex94R/R may be obtained, meeting the demand for high recording density.
Preferably, the composite further includes a nonmagnetic interlayer which separates at least one of the pinned magnetic layer and the free magnetic layer into two sublayers, wherein the two divided sublayers are in a ferri-magnetic state in which magnetization vectors of the two divided sublayers are antiparallel to each other.
When the pinned magnetic layer is divided into two sublayers by a nonmagnetic interlayer, one of the two sublayers pins the magnetic vector of the pinned magnetic layer in a predetermined direction and maintains the pinned magnetic layer in a stable state.
When the free magnetic layer is divided into two sublayers by a nonmagnetic interlayer, an exchange coupling magnetic field is generated between the divided sublayers to be in a ferri-magnetic state. As a result, the magnetic thickness is decreased, and the free magnetic layer rotates in an external field with high sensitivity.
Preferably, in this spin-valve thin-film magnetic element, the thickness of the bias underlayers at the interfaces between the free magnetic layer and the hard bias layers is preferably about 1 nm or less, and more preferably, about 0.5 nm or less.
When the thickness is about 1 nm or less, pinholes are readily formed in the bias under layer. The free magnetic layer and the hard bias layers are magnetically coupled through these pinholes in the bias underlayers at the interfaces. Moreover the magnetic charges accumulated in the two side portions of the free magnetic layer are effectively removed by the above-described exchange interaction, thereby inhibiting the demagnetizing field in the two side portions of the free magnetic layer. Thus, a strong bias magnetic field can be applied from each of the hard bias layers to the free magnetic layer, inhibiting the magnetization vectors in the two side portions of the free magnetic layer from being disordered due to the demagnetizing field which would otherwise occur at the two side portions of the free magnetic layer. As a result, the magnetic domains of the free magnetic layer can be further satisfactorily controlled and the stability of the read waveform at the two ends of the track width Tw can be further improved.
Preferably, the bias underlayers include a nonmagnetic metal having a body-centered cubic structure, and the hard bias layers are made of Cr for the reasons described above.
Slope angles of the side portions of the composite sandwiched by the hard bias layers are preferably about 30 degrees or more to reduce Barkhausen jump (BHJ) to about 15% or less. More preferably, the slope angles are about 45 degrees or more to reduce the BHJ to about 10% or less, and more preferably the slope angles are about 60 degrees or more to reduce the BHJ to about 5% or less.
A thin-film magnetic head equipped with the above described magnetoresistive thin-film magnetic element also provided. In the thin-film magnetic head, the magnetic domains of the free magnetic layer are satisfactorily controlled, Barkhausen noise is prevented, and the stability of the output waveform at the two ends of the track width is improved.
A method for making a magnetoresistive thin-film magnetic element has the steps of: forming a composite layer on a substrate, the composite layer formed of an antiferromagnetic layer, a pinned magnetic layer in contact with the antiferromagnetic layer, a nonmagnetic conductive layer, and a free magnetic layer, wherein the magnetization vector of the pinned magnetic layer is pinned by an exchange coupling magnetic field with the antiferromagnetic layer; applying a lift-off resist on the composite layer; removing the area not covered by the lift-off resist by an ion milling so as to form a substantially trapezoidal composite; forming bias underlayers for controlling the crystal orientation of hard bias layers at the two sides of the composite by at least one process of an ion beam sputtering process, a long-throw sputtering process, and a collimation sputtering process while arranging a first target to oppose the substrate to be parallel to each other or arranging the first target to oppose the substrate so that the angle defined by the first target and the substrate is smaller than the angle defined by a second target and the substrate during the subsequent step of forming the hard bias layers; forming, on the bias underlayers, the hard bias layers for orienting the magnetization vector of the free magnetic layer in the direction substantially orthogonal to the pinned magnetic layer by at least one of an ion beam sputtering process, a long-throw sputtering process, and a collimation sputtering process while arranging the second target to oppose the substrate so that the angle defined by the second target and the substrate is larger than the angle defined by the first target and the substrate during the preceding step of forming the bias underlayers; and forming, on the hard bias layers, conductive layers by at least one of an ion beam sputtering process, a long-throw sputtering process, and a collimation sputtering process while arranging a third target to oppose the substrate so that the angle defined by the third target and the substrate is larger than the angle defined by the second target and the substrate during the preceding step of forming the hard bias layers.
This method may be suitable for making the magnetoresistive thin-film magnetic element, having the bias underlayers provided at the bottom of the hard bias layers, and the magnetoresistive thin-film magnetic element, having the bias underlayers provided at the bottom of the hard bias layers and extending to the interfaces between the free magnetic layer and the hard bias layers.
Preferably, the step of forming the hard bias layers may include optimizing the angle defined by the first target and the substrate so as to form bias underlayers on the substrate at the two sides of the composite and on parts of the side surfaces at the two sides of the free magnetic layer. The hard bias layers are formed so that end portions of the hard bias layers and side portions of the free magnetic layer of the composite contact each other at least partly.
Alternatively, the step of forming the hard bias layers may include optimizing the angle defined by the first target and the substrate so as to form bias underlayers on the substrate at the two sides of the composite and on the side surfaces of the free magnetic layer. The hard bias layers are formed at the interfaces between the two sides of the free magnetic layer of the composite and the end portions of the hard bias layers.
Preferably, during the step of forming the substantially trapezoidal composite, the slope angles at the two side portions of the composite are formed to be about 30 degrees or more for the reasons described above.
Other systems, methods, feature, and advantages of the invention will be or will become apparent to one skilled in the art upon examination of the following section figures and detailed description. All such additional systems, methods, features, and advantages are intended to be included within this description, within the scope of the invention, and protected by the accompanying claims.